Re: Hedghog standards converter
The second modulator IC is only used for the sound, and the input used is the video input, because we need AM modulation.
There is a video clamp on the input (inside the IC), and for this reason the audio circuit (just before the modulator) is made like this, providing an adjustable DC level. The level pot on the sound modulator biases the input to disable the video clamp on the IC.
So far my setting of the carrier pot (in fact the pot to get around the video clamp) about half-way seems to be good.
The audio level control should be set to give sufficient audio, but not more than that. I put in a (very) small pot with a shaft, so that I can adjust this from the outside of the case. Not all sources have the same audio level.
As a kind of reference level, you can use one of the internal test tones Frank has provided.
I still have to compare the hor sync of the Hedghog with other standard converters on various sets.
Jac
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